DE 603 09 400 T2 describes a projection system provided with a plurality of light-emitting elements such as LEDs, for example, downstream of which is arranged in each case an optical integrator, said projection system allowing a projection surface to be illuminated uniformly.
WO 2008/027692 A2 and WO 97/01727 A1 likewise describe the coupling-out of light from a light-emitting element by means of an optical integrator.
The document EP 2211090 A1 discloses a projection system for illuminating a projection surface. The projection system according to EP 2211090 A1 includes light sources, each consisting of a plurality of light-emitting elements. The light elements each emit light having a different wavelength. Light of each light-emitting element is coupled into an entrance opening of an optical integrator of the projection system such that mixed and collimated light of all the light-emitting elements emerges at its exit opening. An imaging optical unit projects the light emerging from the exit opening of each integrator onto the projection surface.
On account of the geometrical conditions and the general laws of optics, this gives rise not only to an imaging of the exit opening of the integrator, but also to an imaging of the entrance opening visible through the integrator, where the light of the light-emitting elements has not yet been mixed. The superimposition of the two imagings on the projection surface impairs the perceived imaging quality.
This is intended to be improved by means of a diffuser provided in EP 2211090 A1. However, the diffuser has the disadvantage of impairing the light efficiency.